HP 9101A Memory Unit


I recently came across a 9101A memory expansion unit for the HP 9100 calculators. I hooked it up to one of my HP 9100B machines, and found that it mostly works but there are some memory locations that always report that they are protected and no amount of fiddling with the settings change this behavior. I have cleaned all of the circuit board connectors and reseated boards with no improvement. I haven't been able to find any service info on this device. Does anyone here have insights into how to go about diagnosis and repair?

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